Method of three-dimensionally culturing chondrocytes

ABSTRACT

It is intended to provide a method of three-dimensionally culturing normal joint chondrocytes; the production and supply of chondrocytes; and a transplantation material to be used in an injured site in a joint tissue.

This Application is a 371 of PCT/JP2005/010038, filed Jun 1, 2005; thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention mainly relates to a method of producingchondrocytes, and to providing a transplantation material to an injuredsite in a cartilage tissue. The present invention also relates to a kitfor studying the cartilage tissue.

BACKGROUND TECHNOLOGY

When a damage or a defect occurs in a joint cartilage due to some cause,it is rare that the joint cartilage is completely restored andregenerated. One of the reasons includes a nature of chondrocyte. Thatis, as the joint chondrocytes are highly differentiated, scarcelyproliferate and differentiate, their restoration capacity is extremelylow. Another reason includes a peripheral inherent environmentsurrounding the chondrocytes. Since a cartilage tissue lacks a nerve anda blood vessel, no restoration mechanism by hemorrhage, inflammation andgranulation is available. Since a periphery of the cartilage tissue issurrounded by extracellular matrix, the chondrocytes can not easilymigrate from a healthy site to the injured site.

The injured site in the joint cartilage induces degradation of itsperiphery and adjacent cartilage with time, finally advances toosteoarthritis, and causes the reduction of joint functions, e.g., painand mobile limitation. Therefore, various therapeutic methods have beendeveloped as methods of restoring the joint cartilage so far, but thisis an actual state that the method of restoring a defect site withcomplete hyaline cartilage has not been well established at present.

Accompanying with the recent advance of cell engineering, regenerationof the cartilage tissue by autologous chondrocytes has been activelyattempted. It is important as a transplantation material applied to theinjured site that enough amount of the chondrocytes are maintained, andthat the retained chondrocytes can produce the sufficient amount of theextracellular matrix.

However, there is a problem that the chondrocytes dedifferentiate intofibroblasts during the culture when the chondrocytes are isolated froman autologous cartilage piece and subsequently grown in a monolayerculture. Thus, it is difficult to culture the chondrocytes keeping withtheir character well. As a scaffolding exhibiting a three dimensionalstructure, biomaterials such as collagen gel sponge, agarose gel,gelatin, chitosan, hyaluronic acid and PGA, PLA and PLGA have beenreported, but no material having strength and frictional coefficientcorresponding to a cartilage matrix has been developed until now, and atransplantation material having the characters close to the jointcartilage tissue has been desired.

DISCLOSURE OF INVENTION Problem to be Solved By The Invention

It is an object of the present invention to provide a method ofculturing chondrocytes and a transplantation material for regenerationof a cartilage tissue in an injured site in the cartilage tissue basedon this method, and a kit for studying the cartilage tissue.

Means For Solving The Problem

As a result of an extensive study in such an actual circumstance, thepresent inventors have found that normal chondrocyte can be grown in agelled-structure comprising collagen and proteoglycan with keeping thecharacters in the absence of various growth factors. The presentinventors also have found that cartilage tissue components produced fromthese chondrocytes reconstruct a new three-dimensional structure similarto the cartilage tissue in the gelled-structure, and provide an idealtransplantation material for regeneration of the cartilage tissue. Byfurther advancing this fact, it is possible to provide a material forstudying the cartilage tissue in future.

That is, it is possible to provide the following inventions.

[1] A method for three-dimensional culture of chondrocytes,characterized by culture condition in which the chondrocytes areembedded in a gelled structure comprising collagen and proteoglycan.

[2] The method according to [1] wherein a ratio of collagen toproteoglycan is 1:0.3 to 1.1 (weight ratio).

[3] A method of chondrocyte production characterized in that thechondrocytes are grown in a gelled structure comprising collagen andproteoglycan.

[4] A gelled-structure comprising collagen and proteoglycan that iscapable of regenerating a cartilage tissue by embedding the chondrocytesin the gelled-structure.

[5] The gelled-structure according to [4] which is a transplantationmaterial to the injured site in a cartilage tissue.

[6] A kit comprising at least chondrocytes, collagen and proteoglycanfor studying a cartilage tissue.

EFFECT OF THE INVENTION

The present invention of three-dimensional chondrocyte culture systemmade it possibles to grow the cells with keeping their characters aschondrocytes and the resulting material thus obtained can be provided asthe caltilage transplantation material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the change of cell numbers when chondrocytes were culturedin a gelled-structure comprising type I atelocollagen and proteoglycan.The ratio of atelocollagen to proteoglycan is A group (1:0), B group(1:0.5), C group (1:0.51) or D group (1:2.56).

FIG. 2 shows the gelled structure stained with hematoxylin and eosinafter the culture. a, b and c represent A group, B group and C group,respectively.

FIG. 3 shows the gelled structure stained with alcian blue after theculture. a, b and c represent A group, B group and C group,respectively.

FIG. 4 shows the gelled-structure immunologically stained for type IIcollagen after the culture. a, b and c represent A group, B group and Cgroup, respectively.

FIG. 5 is a photograph of the gelled structure (A group) on the 56th dayof the culture using a digital camera.

FIG. 6 is a photograph of the gelled structure (C group) on the 56th dayof the culture using the digital camera.

BEST MODES FOR CARRYING OUT THE INVENTION

In one preferable embodiment of the present invention, as chondrocytessubjected to the present invention, the normal chondrocytes present in ajoint tissue can be used, but the chondrocytes obtained from bone marrowcells and mesenchymal stem cells capable of being differentiated andinduced into the chondrocytes can be used. Depending on the purpose, thenormal chondrocytes derived from human beings and animals other than thehuman beings can be used.

Collagen (e.g., types II, III, IV, V, VI, VIII, IX, X or mixturesthereof) is not particularly limited, preferably Type I and Type IIcollagen can be used, and in particular, preferably Type II collagen ora collagen mixture containing Type II collagen can be used.

Collagen is preferably atelocollagen for increasing water solubility,and low molecular weight collagen hydrolyzed with enzyme may be used, ifit is possible to form the scaffoldings with maintaining thethree-dimensional structure. When the transplantation is subjected tothe human being, human-derived collagen is desirable, but collagen isnot particularly limited and collagen derived from the animal other thanthe human being, such as, collagen derived from rabbits, cattle, horsesand mice can be suitably used.

The “gelled-structure” or the “three-dimensional structure” herein meansone capable of embedding the chondrocytes therein, becoming thescaffoldings of the chondrocytes and making the chondrocytes grow in thestructure.

Proteoglycan may be derived from any of the human being and the animalsother than the human being, further proteoglycan derived from fishes orthe large animal may be used in terms of material collection, andproteoglycan derived from mammalian animals such as rabbits, cattle,horses and mice can be suitably used. In the case of using the fishes,proteoglycan isolated from salmon or shark can be used.

The ratio of collagen to proteoglycan is particularly important to makethe chondrocytes grow with keeping the characters of the normalchondrocyte, preferably proteoglycan is in the range of 0.3 to 1.1relative to 1 of collagen in weight ratio, and more suitably it ispreferable that proteoglycan is in the range of about 0.5 to 0.7relative to 1 of collagen.

As culture media for the chondrocytes, it is possible to use the mediaand additives used for the ordinary culture of the chondrocytes or themesenchymal cells without limitation. As the media, for example,RPMI1647, RPMI1640, MEM, BME, 5A, DM120, RITC80-7, F12, L-15, MCDB104and MCDB107 can be suitably used. Upon culture, it is desirable to addserum, a concentration of the serum can be appropriately selectedbetween 1 to 20% depending on the conditions, and suitably the serum canbe used suitably in the range of 5 to 15%, and more suitably in therange of 5 to 10%. As the type of the serum, sera derived from variousanimals can be used without limitation, for example, bovine serum, fetalcalf serum and horse serum can be used.

Collagen and proteoglycan to be used are mixed in the medium at anaforementioned predetermined ratio, and are desirably used in the rangeof the concentration at which they can be gelled and form thethree-dimensional structure. The concentration of collagen is 0.8 to2.4% by weight and preferably 1.2 to 2.0% by weight, and theconcentration of proteoglycan is 0.4 to 1.2% by weight and preferably0.6 to 1.0% by weight. The total concentration of collagen andproteoglycan is about 1.2 to 3.6% by weight and preferably about 1.8 to3.0% by weight. When these concentrations are too low, the gel strengthbecomes insufficient whereas when they are too high, the gel becomesexcessively hard and can not keep the sufficient steric structure.

The gelled structure can be completed by adding the chondrocytes to thegel mixed in this way, stirring to become sufficiently homogenous andthen by dropping or placing on a culture dish.

To stabilize the structure, it is desirable to leave stand in anincubator for about 10 to 30 minutes after dropping or placing themixture on the culture dish. Then, the medium is added to an extent thatthe gelled-structure is submerged and the culture is started. Thisprocedure can be performed according to the collagen drop method(Journal of Hepato-Biliary-Pancreatic Surgery 5(3) 261-268 (1998)), butthe method is not always limited thereto. As the chondrocytes to beused, for example, those collected from the injured site in the jointand separated by the standard methods can be used. The number of cellsto be used is suitably in the range of about 1×10³ to 1×10⁶ cells permL, and more suitably in the range of about 1×10⁴ to 5×10⁵ cells per mL.

It is appropriate that a culture period is about 2 to 8 weeks, and evenif the culture is continued for 8 weeks or more, the cell morphology iskept. Therefore, the culture period can be appropriately determineddepending on the number of the chondrocytes added at the start of theculture. Thus, in this culture condition, the chondrocytes proliferatein the gelled structure with keeping their characters. It is preferableto change the medium every 2 to 4 days, which is within the conditionunder which the ordinary cell culture is performed.

In the joint cartilage tissue, the normal chondrocytes occupy only about2%, and the propotion of extracellular matrix including collagen andproteoglycan is very high. From this point of view, the presence of theextracellular matrix in the joint tissue is important. In the presentculture system, the chondrocytes not only start their proliferation withkeeping their characters but also produce the extracellular matrix. Thatis, the extracellular matrices typically present in the joint tissue,such as type II collagen, a marker of the chondrocyte and proteoglycanare accumulated in the gelled-structure. In this sense, they seem toconstruct a joint-like tissue. Therefore, it is possible to collect thechondrocytes separately from the culture system, and further thegelled-structure containing the joint-like tissue can also be used asthe good transplantation material for the purpose of regenerating thecartilage injury site.

For this regeneration procedure, the joint-like gelled-structure can betransplanted to the injured site by trimming the size and shapeadjusting the injured area.

Since the pseudo-cartilage gelled-structure is reconstructed byextracellular matrices such as type II collagen, proteoglycan andfibronectin produced by the normal chondrocytes, this system isexcellent to provide the useful material for studying the cartilagetissue. Taken together, it is possible to provide a kit comprising thechondrocytes, collagen and proteoglycan for studying the cartilagetissue.

EXAMPLES

The present invention will be described in more detail with reference toExamples. These Examples are described for the purpose ofexemplifications only, and do not limit the present invention.

Example 1

Culture of Chondrocytes

Chondrocytes (purchased from Hokudo Co., Ltd.) isolated from a rabbitknee joint cartilage were used. The chondrocytes obtained after thefirst passage were used for the experiment. A culture medium RPMI 1640containing 10% FBS and 100 μM ascorbic acid (Hokudo Co., Ltd.) was used.A mixture containing following ratio, 3% Type Icollagen:(proteoglycan+culture medium)=65 μL:60 μL was prepared and thechondrocytes (about 1×10⁵)were added thereto (weight ratios ofatelocollagen proteoglycan, A group [1:0], B group [1:0.05], C group[1:0.51] and D group [1:2.56]). Then the mixture was thoroughly stirred,dropped on a 35 mm dish, and gelled by incubating at 37° C. for 10minutes. After confirming that the gel was formed well, 2.5 mL of theculture medium was added. The cells were cultured in 5% CO₂ at 37° C.The medium was changed twice a week, and the culture was performed for21 days.

In the meantime, the cell number was counted on the 7th and 14th daysafter the start of the culture in accordance with the proceduredescribed below. That is, the gel was peeled from the dish andtransferred to another 35 mm dish. The culture medium and collagenase(collagenase S-1, Nitta gelatin) were added to the dish, which was thenincubated at 37° C. for 60 minutes to liberate the cells (FIG. 1). Cellviability was counted using a hemocytometer. The number of the alivecells was confirmed by staining with trypan blue. As a result, the cellnumbers in the A to C groups were increased. In D group, the cell numberwas decreased on the 14th day. Comparing respective groups, the cellnumber in the C group was obviously higher than that in the othergroups.

In the B group, the morphological change to fibroblasts was slightlyobserved. In the D group, no morphological change was observed, but theproliferation was slow and it was also difficult to maintain the gel.

Histological and Immunohistological Evaluation

On the 21st day of the culture, specimens were fixed with 10% formalin,and stained with hematoxylin/eosin or alcian blue. In order to identifythe presence of Type II collagen, an important substrate of the hyalinecartilage, the specimens were immunologically stained using ananti-human type II collagen antibody (Daiichi Fine Chemical Co., Ltd.).FIGS. 2 a, 3 a and 4 a represent the A group, FIGS. 2 b, 3 b and 4 brepresent the B group and FIGS. 2 c, 3 c and 4 c represent the C group.

By the staining studies with hematoxylin/eosin (FIGS. 2 a, b and c) andwith alcian blue (FIGS. 3 a, b and c), a significant increase of thecell number was observed in the C group. In both stainings, thechondrocytes and cartilage spaces were observed, indicating theregeneration of the cartilage tissue. Meanwhile, many spindlebody-shaped cells which were fibroblast-like were observed in the Agroup.

The immunological staining of collagen type II (FIGS. 4 a, b and c)showed the appearance of collagen type II stained with brown color inperipheries of the chondrocytes. In addition, cytoplasmic portions werestained with brown color, suggesting the synthesis of collagen type II.

In the histological evaluation, the cells were identified to proliferatenot in the center of the gel but in peripheries of the gel in common inall groups. Almost no alive cell was identified in the center of the gelin the A and B groups. In the C group, some alive cells were identifiedin the center of the gel compared with the A and B group. In the Dgroup, the gel formation was poor, there seems to be a problem of themixture ratio of collagen and proteoglycan, and thus the D group was notevaluated histologically.

FIGS. 5 (A group) and 6 (C group) show the cultured gel on the 56th dayof the culture. In the A group, the gel tends to shrink and the shapebegins to collapse. A phase contrast microscopic observation showed thatthe spindle-shaped cells were overlaid, speculating that thechondrocytes had altered to fibroblast-like cells. On the other hand, inthe C group, the gel surface was smooth and the shape of the gel waskept well. The phase contrast microscopic observation showed that thecircular cells were overlaid, indication that the chondrocytesproliferate with keeping their characters.

1. A method for three-dimensional culture of chondrocytes, characterizedby culture condition in which the chondrocytes are embedded in a gelledstructure prepared by mixing collagen and proteoglycan, dropped on aculture dish and gelled, wherein a ratio of collagen to proteoglycan is1:0.3 to 1:1.1 by weight, wherein the concentration of collagen is 0.8to 2.4% by weight and the concentration of proteoglycan is 0.4 to 1.2%by weight, and wherein collagen is selected from the group consisting ofatelocollagen and low molecular weight collagen hydrolyzed with enzyme.2. A method of chondrocyte production characterized in that thechondrocytes are grown in a gelled structure prepared by mixing collagenand proteoglycan, dropped on a culture dish and gelled, wherein a ratioof collagen to proteoglycan is 1:0.3 to 1:1.1 by weight, wherein theconcentration of collagen is 0.8 to 2.4% by weight and the concentrationof proteoglycan is 0.4 to 1.2% by weight, and wherein collagen isselected from the group consisting of atelocollagen and low molecularweight collagen hydrolyzed with enzyme.